A follow-up study of cancer risk in 145,000 x-ray technologists is ongoing. Overall, cancer mortality was 21% lower than expected, but approached normal levels after about 30 years following certification. Neither lung cancer nor leukemia mortality were associated with number of years worked in the medical radiation field or with specific work practices. Breast cancer mortality rates were similar to those in general population, however, a significant 30% excess was observed relative to all other cancers. A study of BRCA1 mutations in technologists diagnosed with breast or ovarian cancer supported evidence that about 10% of very early onset breast cancer cases may have germline alterations. Chromosome aberrations in circulating lymphocytes, identified using flourescent in-situ hybridization (FISH), correlated closely with number of years worked but not with documented doses from the nation's largest commercial dosimetry company, Landauer Inc. Film badge readings, available for 90,000 technologists from Landauer, will be used in conjunction with FISH results and work history data to reconstruct dose estimates for individual technologists. Cancer incidence is being evaluated in three cohorts, comprising 17,500 clean-up workers, from Estonia, Latvia, and Lithuania who were sent to Chernobyl (Ukraine) following the reactor accident in 1986. Cohort members are interviewed to elicit other risk factor information. In addition, with support from DOE, NRC, and the Institut de Protection et Surete Nucleaire (IPSN), NCI has organized a pilot study of leukemia and other hematologic disease among the Chernobyl clean-up workers in Ukraine. A cohort of 20,000 nuclear workers chronically exposed to large doses of external radiation and/or plutonium at the Mayak nuclear weapons plant in the South Ural region in Russia is being studied to evaluate cancer mortality.